The present invention relates generally to an illumination and imaging system for a full-frame document reproduction machine and, more particularly, to an integral assembly which combines a full-frame document illumination source and an array of short focal length projection lenses.
Prior art full-frame document illumination and imaging systems generally employ a flash lamp combined with a conventional projection lens to provide full-frame exposure of a document at a photosensitive image plane. Representative systems are disclosed in U.S. Pat. Nos. 3,697,177 (Booth) and 4,333,723 (Green et al). These prior art systems offer relatively fast throughput compared to the conventional scan/rescan systems but the flash and projection lens components are relatively expensive. These full-frame flash systems also have relatively long total conjugates and require sizeable housing units to enclose the system components.
There are many document reproduction applications which would benefit from a relatively inexpensive, full-frame, illumination system combined with a short conjugate imaging system. Heretofore, this configuration has not been possible. Short focal length projection, or transmission, systems are known in the art in a linear scan configuration wherein a lamp/lens assembly is moved relative to a document in an object plane to produce a line-by-line flowing image at a photoconductive image plane. U.S. Pat. No. 3,544,190 discloses a system where a moving lens strip imaging system scans beneath a fixed document platen. In U.S. Pat. No. 3,947,106, the imaging array is comprised of a plurality of gradient index optical fibers bundled into a two-row configuration. For these prior art scan systems, linear lamps are used to incrementally illuminate a document placed at the object plane.
A full-frame, two-dimensional microlens configuration has been disclosed in a paper presented July 4, 1983 at the 4th Topical Meeting On "Gradient-Index Optical Imaging Systems". This paper is printed on pages 224-227 of the Technical Digest of that conference. This article does not disclose any practical way to utilize such a lens in a document reproduction device since there is no means for providing the requisite document illumination. It would be desirable to combine the high throughput characteristic associated with full-frame illumination systems with the compactness and favorable economics associated with short focal length imaging systems. This objective has been realized in the present invention by forming a short focal length imaging system as a full-frame array and integrating an illumination source into the body of the array. This configuration, when appropriately positioned beneath a document platen, permits the entire document to be illuminated in a full-frame illumination mode. Reflected light is then projected by the full-frame lens array onto the surface, for example, of a flat photoreceptor. More specifically, the present invention is directed towards an imaging system for transmitting an image of a document at an object plane onto a photosensitive image plane, the system including a full-frame imaging and illumination device positioned between said object and image planes, said device comprising:
a plurality of short focal length lens elements assembled to form a full-frame lens array, PA1 an addressable light source positioned in at least some of the interstitial spaces separating said lens elements and on the surface of the array adjacent said object plane, and PA1 means to activate said light source whereby light produced by said light source is directed to said document, reflected therefrom and projected by said lens array onto said image plane to form a latent image of said document on said image plane.